The present invention relates to network communications and more particularly, to an adaptive transmission system used in a network.
Modern society continues to create exponentially increasing demands for digital information and the communication of such information between data devices. Local area networks use a network, cable or other media to link stations on the network for exchange of information in the form of packets of digital data. A typical local area network architecture uses a media access control (MAC) enabling network interface cards at each station to share access to the media. Most conventional local area network architectures use media access controllers operating according to half-duplex or full-duplex Ethernet (ANSI/IEEE standard 802.3) protocol and a prescribed network medium, such as twisted pair cable.
These architectures have proven quite successful in providing data communications in commercial applications. However, these common local area network architectures require installation of specialized wiring and use of specific wiring topologies. For example, the most popular network protocols, such as Ethernet, require special rules for the wiring, for example with regard to quality of wire, range of transmission and termination.
Due to the success of the Internet and the rapid decreases in the prices of personal computers and associated data equipment, a demand has arisen for data communications between a limited number of devices within relatively small premises, typically a residence or small business. While existing local area networks can serve the purpose, in such installations, the cost of installing physical network wiring satisfying the rules for the particular protocol can be prohibitively expensive.
Most existing buildings, including residences, include some existing wiring, for phones, electrical power and the like. Proposals have been made to communicate data using such existing infrastructure. This reduces the costs of wiring for the network, but the existing wiring raises a variety of issues regarding transport of high-speed digital signals.
For example, efforts are underway to develop an architecture that enables computers to be linked together using conventional twisted pair telephone lines. Such an arrangement, referred to herein as a home network environment, provides the advantage that existing telephone wiring in a home may be used to implement a home network environment without incurring costs for substantial new wiring installation. However, any such network must deal with issues relating to the specific nature of in-home telephone wiring, such as operation over a media shared with other services without interference from or interfering with the other services, irregular topology, and noise. With respect to the noise issue, every device on the telephone line may be a thermal noise source, and the wiring may act much like an antenna to pick up disruptive radio signal noise. Telephone lines are inherently noisy due to spurious noise caused by electrical devices in the home, for example dimmer switches, transformers of home appliances, etc. In addition, the twisted pair telephone lines suffer from turn-on transients due to on-hook and off-hook and noise pulses from the standard telephones coupled to the lines, and electrical systems such as heating and air conditioning systems, etc.
An additional problem in telephone wiring networks is that the signal condition (i.e., shape) of a transmitted waveform depends largely on the wiring topology. Numerous branch connections in the twisted pair telephone line medium, as well as the different associated lengths of the branch connections, may cause multiple signal reflections on a transmitted network signal. Telephone wiring topology may cause the network signal from one network station to have a peak-to-peak voltage on the order of 10 to 20 millivolts, whereas network signals from another network station may have a value on the order of one to two volts. Hence, the amplitude and shape of a received pulse may be so distorted that recovery of a transmit clock or transmit data from the received pulse becomes substantially difficult.
At the same time a number of XDSL technologies are being developed and are in early stages of deployment, for providing substantially higher rates of data communication over twisted pair telephone wiring of the telephone network. XDSL is used herein as a generic term for a group of higher-rate digital subscriber line communication schemes capable of utilizing twisted pair wiring from an office or other terminal node of a telephone network to the subscriber premises. Examples under various stages of development include ADSL (Asymmetrical Digital Subscriber Line), HDSL (High data rate Digital Subscriber Line) and VDSL (Very high data rate Digital Subscriber Line).
Consider ADSL as a representative example. For an ADSL-based service, the user""s telephone network carrier installs one ADSL modem unit at the network end of the user""s existing twisted-pair copper telephone wiring. Typically, this modem is installed in the serving central office or in the remote terminal of a digital loop carrier system. The user obtains a compatible ADSL modem and connects that modem to the customer premises end of the telephone wiring. The user""s computer connects to the modem. The central office modem is sometimes referred to as an ADSL Terminal Unitxe2x80x94Central Office or xe2x80x98ATU-Cxe2x80x99. The customer premises modem is sometimes referred to as an ADSL Terminal Unitxe2x80x94Remote or xe2x80x98ATU-Rxe2x80x99. The ADSL user""s normal telephone equipment also connects to the line through a frequency combiner/splitter, which is incorporated in the ATU-R. The normal telephone signals are split off at both ends of the line and processed in the normal manner.
For digital data communication purposes, the ATU-C and ATU-R modem units create at least two logical channels in the frequency spectrum above that used for the normal telephone traffic. One of these channels is a medium speed duplex channel and the other is a high-speed downstream only channel. Two techniques are under development for dividing the usable bandwidth of the telephone line to provide these channels. One approach uses Echo Cancellation. Currently, the most common approach is to divide the usable bandwidth of a twisted wire pair telephone line by frequency, that is to say by Frequency Division Multiplexing (FDM).
FDM uses one frequency band for upstream data and another frequency band for downstream data. The downstream path is then divided by time division multiplexing into one or more high-speed channels and one or more low speed channels. The upstream path also may be time-division multiplexed into corresponding low speed channels.
The FDM data transport for ADSL services utilizes discrete multi-tone (DMT) technology. A DMT signal is basically the sum of N independently quadrature amplitude modulated (QAM) signals, each carried over a distinct carrier frequency channel. The frequency separation between consecutive carriers is 4.3125 KHz with a total number of 256 carriers or tones (ANSI). An asymmetrical implementation of this 256 tone-carrier DMT coding scheme might use tones 32-255 to provide a downstream channel of approximately 1 MHz analog bandwidth. In such an implementation, tones 8-31 are used as carriers to provide an upstream channel of approximately 100 kHz analog bandwidth. Each tone is QAM to carry up to 15 bits of data on each cycle of the tone waveform (symbol). An example of a conventional DMT-based system is illustrated in FIG. 1.
The existing DSL systems provide effective high-speed data communications over twisted pair wiring between customer premises and corresponding network-side units, for example located at a central office of the telephone network. The DSL modem units overcome many of the problems involved in data communication over twisted pair wiring. However, for a number of reasons, the existing DSL units are not suitable to providing local area network type communications within a customer""s premises. For example, existing ADSL units are designed for point-to-point communication. That is to say, one ATU-R at the residence communicates with one ATU-C unit on the network end of the customer""s line. There is no way to use the units for multi-point communications. Also, the existing ADSL modems tend to be quite complex, and therefore are too expensive for in-home communications between multiple data devices of one customer.
As described above, multi-point networks using conventional technology are not suitable for in-home use. Additionally, even conventional multi-point networks requiring specialized wiring and having predetermined topologies often suffer from poor signal quality between two or more nodes in the network.
For example, the medium connecting two particular nodes may be of poor quality resulting in drastic signal attenuation and phase distortion. The attenuation and distortion often lead to data errors when transmitting the data over such a medium. Prior art systems often retransmit the data when errors occur. However, when the errors are caused by the communications medium or the network layout, simply retransmitting the data often results in another erroneous transmission.
There is a need for an arrangement that provides an adaptive data transmission system for use in a network.
There is also a need for an arrangement that provides an adaptive data transmission system for use in a network employing discrete multi-tone technology.
These and other needs are met by the present invention, where a data transmission device used in a network node includes a transmitter portion and a receiver portion. The transmitter transmits a data packet to a receiving node. When the data is received without errors, the receiving node transmits an acknowledgement signal to the transmitting node and the transmitting node is ready to transmit the next packet. However, when an error in transmission occurs, the transmitting node is able to retransmit a portion of the data, along with at least one redundant copy of the portion. If at least one of the redundant data portions is received without errors, an acknowledgement is sent back to the transmitting node. If errors still occur, the transmitting node is able to continue to reduce the number of bits sent and increase the amount of redundancy data until an error-free transmission occurs.
According to one aspect of the invention a device is configured to transmit and receive data over a communications medium. The device includes a transmitter configured to transmit a first packet comprising bits of data. The device also includes a receiver configured to receive an acknowledgement signal from a destination node indicating that the first packet was received without errors. The transmitter is further configured to transmit a second packet comprising a first plurality of portions, when the acknowledgement signal is not received. The first plurality of portions each include the same predetermined bits of the first packet.
Another aspect of the present invention provides a method of transmitting data from a network node. The method includes transmitting a first packet comprising bits of data. The method also includes receiving an acknowledgement signal from a destination node when the first packet was received without errors. The method further includes transmitting a second packet comprising a first plurality of portions, when the acknowledgement signal is not received within a preset period of time. The plurality of portions each include the same predetermined bits of the first packet.
Other advantages and features of the present invention will become readily apparent to those skilled in this art from the following detailed description. The embodiments shown and described provide illustration of the best mode contemplated for carrying out the invention. The invention is capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawings are to be regarded as illustrative in nature, and not as restrictive.